Please do remember. A glass jar is inert. No chemical will be able to react to it under normal and extreme conditions – unless the glass itself is melted. Glass can be reused a hundred times, thousands times and to infinity as long as it is whole and sound. A bottle cap is disposable though. A new one should be provided every processing session. So every glass jar is considered capless after consuming the package content.
Decent and crazy ways to cap it again.
1) Buy a new screw cap. It’s the best thing to do. Contact a trusted supplier and procure new sterile caps. A must if the package food is for commercial sale.
Every cap has a rubber seal underneath. It makes contact with the jar lid making and airtight and watertight closure. Reusing is not practiced because 1) the pressure between the jar lid and metal might have damage the rubber seal and 2) the food components might have migrated to rubber seal, it might ruin the next food content.
Next items are recommended only for home use…
2) Reuse/Recycle. Just recycle the cap together with the glass bottle. Wash both thoroughly and dry before using. Make sure the cap has no indelible stain, rust and foul odor. Check for leaks by capping and inverting the bottle. Discard if leaking.
3) From other used jar. Same as previous item but get the cap from other jar of the same mouth type. Do if the provided cap does not fit for reuse.
4) Rubber band and plastic. The last resort. Fit a clean plastic bag around the jar mouth and secure with a rubber band. For strict home use only, should not be use for resale.